Perhaps you should try some spelling variations:
vanh dai » van dai, vanh tai, lanh dao
sach ky » sach y, sach ty, sach kem
hieu va » lieu va, hieu qua
cac luc » cau luc, coc luc, cac nuoc
va vanh » va van, va danh, va hanh
dai huu » dao huu, dai hau, dai thua
huu tre » huu tri, cuu tre, huu them
sac ky » cac ky, sai ky
ro hoc » mo hoc, o hoc, so hoc
luc va » duc va, tuc va, loc va

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: su ((sach ky) or (sac ky)) nang ((ro hoc) OR (co hoc)). hieu va cac luc va vanh dai huu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su ((sach ky) OR (sac ky)) nang ((ro hoc) OR (co hoc)). hieu va cac luc va vanh dai huu tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su ((sach ky) or (sac ky)) nang ((ro hoc) OR (co hoc)). hieu va cac luc va vanh dai huu tre*".